Data Whitening in Base-band to Reduce PSD of UWB Signals
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Transcript of Data Whitening in Base-band to Reduce PSD of UWB Signals
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 2
IEEE 802.15-03/121r1
Submission
Data Whitening in Base-band to Reduce PSD of UWB Signals
Shaomin Mo
Panasonic Information and Networking Technologies Laboratories
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 3
IEEE 802.15-03/121r1
Submission
Overview
• Power Spectra Density (PSD) issue in UWB• Analysis of PSD of UWB signals• Mechanisms to reduce PSD
– Phase reversion to reduce PSD– Architecture of using Linear Feedback Shift
Register– Phase reversion for SYNC
• Conclusion
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 4
IEEE 802.15-03/121r1
Submission
PSD is an Important Issue in UWB Communication Systems
• FCC limited authorization of UWB technology, Feb 14, 2002
• Use in restrict spectrum at restrict power• Do not interfere with other wireless systems• Other agencies still have some reservations
about whether UWB will interfere with other wireless systems such as cellular, air navigation and landing systems
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 5
IEEE 802.15-03/121r1
Submission
Emission Levels for GSM & TDMA in the Cellular Receiver Bands
Technology Frequency Range
(mobile RX) (MHz)
Emission Level (dBm),
Bandwidth (kHz)
Average Level
(dBm/MHz)
Part 15 Limit (dBm/MHz)
TDMA 869 – 894
1930 – 1990
-80 dBm, 30kHz
-80 dBm, 30kHz
-64.8
-64.8
-40.0
-53.3 indoor
-63.3 hand-held
GSM 869 – 894
1930 – 1990
-79 dBm, 100kHz
-71 dBm, 100kHz
-69.0
-61.0
-40.0
-53.3 indoor
-63.3 hand-held
Source: “Ultra-Wideband Radio – The New Part 15”, Microwave Journal, February 2003
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 6
IEEE 802.15-03/121r1
Submission
Containing PSD is an Important Part in UWB System Design
• Repeat pulse trains may generate strong line spectra and high PSD
• Traditional scramblers are not sufficient to contain PSD
• PSD suppression leads to– Prevention of interference to existing systems– Potential increase in rate, Tx power (distance)
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 7
IEEE 802.15-03/121r1
Submission
• Signal model
• Probability function of an
Model of Repeat Pulse Train
n
cn nTtwats )()(
1,1
1,}Pr{
n
nn ap
apa
Tc TcTc
t t+1 t+2 t+3
. . .
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 8
IEEE 802.15-03/121r1
Submission
• Ps is determined by w(t) and Tc• Ps is not affected by Pr{an}
• Total PSD is determined by w(t) and Tc• Total PSD is not affected by Pr{an}
PSD of Repeat Pulse Train
pTk
kp
s cdffWdttwT
P222
)()(1
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 9
IEEE 802.15-03/121r1
Submission
PSD of repeat pulse trains consists of • Sc(f) – continuous component• Sd(f) – discrete component
PSD of Repeat Pulse Train
lD
d
c
Tc
lf
Tc
lW
Tc
pfS
pfWTc
fS
)(|)(|)12(
)(
)12(1|)(|1
)(
22
2
22
W(f)
Tcp
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 10
IEEE 802.15-03/121r1
Submission
• W(f) – pulse shape & Tx power• Tc – clock period or pulse rate• p – probability in distribution function
– Does not affect total PSD– Changes distribution of PSD between continuous
and discrete components
Parameters that Determine PSD
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 11
IEEE 802.15-03/121r1
Submission
Simplified Form of PSD
lD Tc
lf
Tc
lW
TcfB
fWTc
fA
)(|)(|1
)(
|)(|1
)(
2
2
2
2
)12(1)(
)12()(
ppD
ppC
)()(),(
)()(),(
pCfBpfS
pDfApfSd
c
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 12
IEEE 802.15-03/121r1
Submission
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
p
C(p)D(p)
Relationship between Continuous and Discrete Components
)()(),(
)()(),(
pCfBpfS
pDfApfSd
c
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 13
IEEE 802.15-03/121r1
Submission
• Because total PSD is constant
A(f) = B(f)
Max(Sc(f)) = Max(Sd(f))
Relationship between Continuous and Discrete Components
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 14
IEEE 802.15-03/121r1
Submission
• Total continuous PSD equals total discrete PSD
• The continuous distributes on all frequencies• The discrete distributes on those discrete
frequencies separated by 1/Tc.
• Continuous PSD is lower than that of discrete PSD on the same frequency components
Relationship between Continuous and Discrete Components
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 15
IEEE 802.15-03/121r1
Submission
PSD with Different p Has Same Envelop but Different Level
0 100 200 300 400-50
-40
-30
-20
-10
0(a): PSD of one pulse
0 100 200 300 400-40
-30
-20
-10
0
10(b): PSD of pulses for p=0.25
0 100 200 300 400-40
-30
-20
-10
0
10(c): PSD of pulses for p=0.5
0 100 200 300 400-30
-20
-10
0
10
20(d): PSD of pulses for p=1
PSD of single pulse P = 0.25
P = 0.5 P = 1.0Line spectra
peak = 15
peak = 9
peak = 3
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 16
IEEE 802.15-03/121r1
Submission
• Contain PSD
• Reduce or eliminate discrete component of PSD reduce PSD across whole spectrum
• Make
Objective of Design
1,5.0
1,5.0}Pr{
n
nn a
aa
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 17
IEEE 802.15-03/121r1
Submission
TDMA Systems
• Traditional communication systems require randomness inside a frame for timing recovery, equalization, etc.
frame N frame N+2frame N+1 . . .
Tc Tc
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 18
IEEE 802.15-03/121r1
Submission
New Requirements to UWB Communication Systems
• Traditional: randomness in X direction• UWB: randomness in both X & Y directions
frame N
frame N+3
frame N+2
frame N+1
offset m
X
Y
blo
ck
s i
n T
DM
A
b its inside a block
Tc
Tc
Tc
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 19
IEEE 802.15-03/121r1
Submission
PSD Analysis: if data is not evenly distributed in Y direction, line spectra appear
• Phase
0 10 20 30 40 50 60-1
-0.5
0
0.5
1(a): Waveform of single pulses
0 100 200 300 400-1
-0.5
0
0.5
1(b): Waveform of data
0 500 1000 1500-60
-50
-40
-30
-20
-10(c): PSD of single pulse
0 500 1000 1500-30
-20
-10
0
10
20(d): PSD of data
Waveform of single pulse Waveform of data
PS of single pulse PSD of data
Original stream: line spectra
& peak = 17
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 20
IEEE 802.15-03/121r1
Submission
Propose 1: Phase Reversion to Reduce PSD
• A random sequence {bn} is generated with
• cn = an ^ bn. It can be shown that
• {cn} is used as the new data for transmission.
1,5.0
1,5.0}Pr{
n
nn b
bb
1,5.0
1,5.0}Pr{
n
nn c
cc
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 21
IEEE 802.15-03/121r1
Submission
Using proposed scheme, line spectra is eliminated and PSD is reduced
0 10 20 30 40 50 60-1
-0.5
0
0.5
1(a): Waveform of single pulses
0 100 200 300 400-1
-0.5
0
0.5
1(b): Waveform of data
0 500 1000 1500-60
-50
-40
-30
-20
-10(c): PSD of single pulse
0 500 1000 1500-40
-30
-20
-10
0
10(d): PSD of data
Waveform of single pulse Waveform of data
PS of single pulse PSD of data
Proposed 1: PSD of cn, Line spectra gone
peak reduced to 8
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 22
IEEE 802.15-03/121r1
Submission
Major Challenge in Implementing Phase Reversion
• Simple way to generate random sequence
• Easy way to synchronize random number generators in both transmitters and receivers
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 23
IEEE 802.15-03/121r1
Submission
Propose 2: Architecture of LFSR
• LFSR stands for Linear Feedback Shift Registers
• Easy implementation• Very suitable for semiconductor
implementation
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 24
IEEE 802.15-03/121r1
Submission
LFSR is loaded with a RN per frame & updated per pulse
NX
OR
1 2 43 25 26 2827.
random num bers (RN)
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 25
IEEE 802.15-03/121r1
Submission
Synchronization of LFSR
• Initial system channel access– Random vectors are generated in advance &
stored in an array– Transmitters & receivers keep same array– Index to a vector in the array is put in data to
transmit
• Initial traffic channel access– Sequence number can be used
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 26
IEEE 802.15-03/121r1
Submission
15-bit LFSR vs. Idea Low Bound
• LFSR is too short• Strong line spectra exist
0 5 10
x 104
-10
0
10
20
30(1-a): PSD of proposed: 10
0 5 10
x 104
-20
-10
0
10
20(1-b): PSD of random: 10
0 5 10
x 104
-20
-10
0
10
20(2-a): PSD of proposed: 50
0 5 10
x 104
-20
-10
0
10
20(2-b): PSD of random: 50
0 5 10
x 104
-20
-10
0
10
20(3-a): PSD of proposed: 200
0 5 10
x 104
-30
-20
-10
0
10(3-b): PSD of random:200
Phase controlled by RNs as
reference of low bound
Proposed LFSR implementation
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 27
IEEE 802.15-03/121r1
Submission
0 5 10
x 104
-20
-10
0
10
20(1-a): PSD of proposed: 10
0 5 10
x 104
-20
-10
0
10
20(1-b): PSD of random: 10
0 5 10
x 104
-20
-10
0
10
20(2-a): PSD of proposed: 50
0 5 10
x 104
-20
-10
0
10
20(2-b): PSD of random: 50
0 5 10
x 104
-30
-20
-10
0
10(3-a): PSD of proposed: 200
0 5 10
x 104
-30
-20
-10
0
10(3-b): PSD of random:200
28-bit LFSR vs. Idea Low Bound• LFSR is long enough• Line spectra is suppressed• Very close to reference
Phase controlled by RNs as
reference of low bound
Proposed LFSR implementation
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 28
IEEE 802.15-03/121r1
Submission
Propose 3: Phase Reversion on SYNC
Three mechanisms can be used:• Phase reversion on the whole SYNC• SYNC is divided into symbols & phase
reversion on symbols• Phase reversion & scrambling on symbols
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 29
IEEE 802.15-03/121r1
Submission
Phase Reversion on SYNC/symbols can eliminate line spectra but not ripples in PSD
0 100 200 300 400-1
-0.5
0
0.5
1(a): Waveform of one symbol
0 500 1000 1500-40
-30
-20
-10
0
10(b): PSD of one symbol
0 500 1000 1500-10
0
10
20
30
40(c): PSD of symbol: p=1
0 500 1000 1500-30
-20
-10
0
10
20(d): PSD of symbol: p=0.5
One cycle of symbols
PSD with phase reversionPSD without phase reversion
Waveform of symbols
Propose 3: line spectra goneOriginal: strong
line spectra
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 30
IEEE 802.15-03/121r1
Submission
Scramble Symbols
Fram e N: 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 0 , ...
Fram e N+7: 7, 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , ...
Fram e N+6: 6, 7 , 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 0 , 1 , 2 , 3 , 4 , 5 , 6 , ...
Fram e N+5: 5, 6 , 7 , 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 0 , 1 , 2 , 3 , 4 , 5 , ...
Fram e N+4: 4, 5 , 6 , 7 , 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 0 , 1 , 2 , 3 , 4 , ...
Fram e N+3: 3, 4 , 5 , 6 , 7 , 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 0 , 1 , 2 , 3 , ...
Fram e N+2: 2, 3 , 4 , 5 , 6 , 7 , 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 0 , 1 , 2 , ...
Fram e N+1: 1, 2 , 3 , 4 , 5 , 6 , 7 , 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 0 , 1 , ...
X
Y
Fram e N+9: 1, 2 , 3 , 4 , 5 , 6 , 7 , 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 0 , 1 , ...
Fram e N+8: 0, 1 , 2 , 3 , 4 , 5 , 6 , 7 , 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 0 , ...
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 31
IEEE 802.15-03/121r1
Submission
Phase Reversion & Scrambling on SYNC/symbols can smooth ripples & eliminate line: snap shot at 10,
50 200 runs
0 1000 2000 3000-30
-20
-10
0
10
20(1-a): PSD using 8 symbols: 1
0 1000 2000 3000-30
-20
-10
0
10
20(1-b): PSD of random pulses: 1
0 1000 2000 3000-40
-30
-20
-10
0
10(2-a): PSD using 8 symbols: 10
0 1000 2000 3000-40
-30
-20
-10
0
10(2-b): PSD of random pulses: 10
0 1000 2000 3000-40
-30
-20
-10
0
10(3-a): PSD using 8 symbols: 50
0 1000 2000 3000-40
-30
-20
-10
0
10(3-b): PSD of random pulses: 50
Proposed 3: PSD of symbol-based phase reversion & scrambling Very close to reference
Phase controlled by RNs as reference of low bound
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 32
IEEE 802.15-03/121r1
Submission
Conclusion
• Phase reversion can effectively reduce PSD• Phase reversion can be applied to PAM,
PPM, Time-Hopping to reduce PSD• LFSR is an easy way to generate RNs with
good performance• Scrambling can enhance performance by
smoothing ripples in PSD with extra processing & can be extended beyond SYNC
March 2003
Shaomin Mo, Panasonic -- PINTLSlide 33
IEEE 802.15-03/121r1
Submission
Thank you